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North Carolina approves Duke Energy’s controversial green tariff plan

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Wednesday, August 14, 2024

A question of ​‘regulatory surplus’ For large customers with 100% clean energy commitments, a green tariff is a necessity in North Carolina, where Duke has a monopoly and cities, data centers, and the like can’t buy clean energy directly from solar farms. In theory, a green tariff allows a company such as Google or Amazon to spur a new supply of clean energy equal to its electric demand, with Duke acting as an administrative go-between. An earlier iteration of Green Source Advantage more or less did just that. But the accounting got more complicated in 2021, when a bipartisan state law required Duke to cut its carbon pollution by at least 95% by 2050. If the company is legally required to build scores of solar farms anyway, can a large customer legitimately claim its sponsorship of one project makes a difference? This question of ​“regulatory surplus” sparked a flurry of arguments and counterarguments before the commission for some 18 months. Duke initially claimed such ​“additionality” was neither feasible nor necessary, and some businesses said chipping in to support the clean energy transition was good enough for them. More than a dozen local chambers of commerce and potential customers wrote to regulators in support of the original program. But Google, the U.S. Department of Defense, and other large customers joined clean energy advocates to flag the problem of regulatory surplus, as did the Center for Resource Solutions, the nonprofit that certifies voluntary renewable energy purchase programs. Duke University, which has no connection to the utility, said it wouldn’t participate in the tariff. ‘A small step in the right direction’  The debate, along with prodding from commissioners, prompted Duke Energy to add a ​“resource acceleration option” to its proposal. The alternative allows large customers to advance about 150 megawatts of solar energy each year by sponsoring projects not selected in the company’s annual competitive bidding process. Every two years, Duke gets retroactive credit for this ​“extra” solar as part of its compliance with the 2021 law.Clean energy advocates believe the new option is a ​“small step in the right direction.” But they note it accounts for 1 gigawatt of clean energy over 10 years, a fifth of the entire program. Customers who lay claim to the remaining 4 gigawatts would not be impacting the state’s transition to clean electricity, they say. ​“If you’re the customer of a business who claims to support our state’s clean energy transition by participating in the program, you’re going to expect that business to be making a difference — not just subsidizing what Duke was going to do anyway,” said Nick Jimenez, senior attorney at the Southern Environmental Law Center. The Carolinas Clean Energy Business Alliance, a group of clean energy suppliers, also criticized the acceleration option. And though the Carolina Utility Customers Association, another group of large industrial customers, didn’t oppose the amended proposed tariff, it registered skepticism. “[Our] members have little interest in the Resource Acceleration Option,” the group said in a letter to regulators, ​“which would deliver electricity at a premium cost without providing the benefit of regulatory surplus-based environmental attributes that would be useful in meeting corporate environmental, social, and governance goals.” Cause for hope?  While advocates see little good in the commission’s approval of the Green Source Advantage Choice program, they still have some faint cause for hope. One is the so-called Clean Transition Tariff, which Duke could propose later this year. An outgrowth of a May agreement between the utility and Amazon, Google, Microsoft, and Nucor, that program could allow participating customers to spur new projects, such as solar–battery storage combos or small nuclear energy, that provide carbon-free electricity around the clock. ​“This is not within the order,” said Jimenez, but the May memorandum of understanding, ​“is the big opportunity for something better.” Duke says the Clean Transition Tariff would be another voluntary option for customers, not a replacement for the one just greenlighted. ​“We see the approval of Green Source Advantage Choice as a first step,” the company’s Stewart said, ​“enabling us to move forward with new tariffs like the Clean Transition Tariff.” Maggie Shober, research director at the Southern Alliance for Clean Energy, agrees the memorandum of understanding is cause for some optimism. But she also notes that it’s only ​“an agreement to talk about something. It could be an opportunity,” she said, ​“or it could be a missed opportunity. “ And no matter what, the Clean Transition Tariff won’t cater to municipalities and other midsize customers with climate commitments. If these customers decline to pursue Green Source Advantage Choice, their only option is to wait for Duke to adjust. Commissioner Jeffrey A. Hughes pointed to that possibility in a concurring opinion. ​“Once the program offerings are launched, it will quickly become clear whether the program is as attractive as Duke asserts,” Hughes wrote. ​“If concerns continue and interest is modest from the outset, it is my hope that Duke will work quickly on new programs that will have a greater impact.”

This story was first published by Energy News Network . North Carolina regulators have approved a controversial green tariff proposal from Duke Energy, rejecting protests from critics who argue it won’t bolster the company’s transition to zero-carbon electricity. Originally designed as a way for large electric…

A question of regulatory surplus’

For large customers with 100% clean energy commitments, a green tariff is a necessity in North Carolina, where Duke has a monopoly and cities, data centers, and the like can’t buy clean energy directly from solar farms.

In theory, a green tariff allows a company such as Google or Amazon to spur a new supply of clean energy equal to its electric demand, with Duke acting as an administrative go-between. An earlier iteration of Green Source Advantage more or less did just that.

But the accounting got more complicated in 2021, when a bipartisan state law required Duke to cut its carbon pollution by at least 95% by 2050. If the company is legally required to build scores of solar farms anyway, can a large customer legitimately claim its sponsorship of one project makes a difference?

This question of regulatory surplus” sparked a flurry of arguments and counterarguments before the commission for some 18 months. Duke initially claimed such additionality” was neither feasible nor necessary, and some businesses said chipping in to support the clean energy transition was good enough for them. More than a dozen local chambers of commerce and potential customers wrote to regulators in support of the original program.

But Google, the U.S. Department of Defense, and other large customers joined clean energy advocates to flag the problem of regulatory surplus, as did the Center for Resource Solutions, the nonprofit that certifies voluntary renewable energy purchase programs. Duke University, which has no connection to the utility, said it wouldn’t participate in the tariff.

A small step in the right direction’ 

The debate, along with prodding from commissioners, prompted Duke Energy to add a resource acceleration option” to its proposal. The alternative allows large customers to advance about 150 megawatts of solar energy each year by sponsoring projects not selected in the company’s annual competitive bidding process. Every two years, Duke gets retroactive credit for this extra” solar as part of its compliance with the 2021 law.

Clean energy advocates believe the new option is a small step in the right direction.” But they note it accounts for 1 gigawatt of clean energy over 10 years, a fifth of the entire program. Customers who lay claim to the remaining 4 gigawatts would not be impacting the state’s transition to clean electricity, they say.

If you’re the customer of a business who claims to support our state’s clean energy transition by participating in the program, you’re going to expect that business to be making a difference — not just subsidizing what Duke was going to do anyway,” said Nick Jimenez, senior attorney at the Southern Environmental Law Center.

The Carolinas Clean Energy Business Alliance, a group of clean energy suppliers, also criticized the acceleration option. And though the Carolina Utility Customers Association, another group of large industrial customers, didn’t oppose the amended proposed tariff, it registered skepticism.

“[Our] members have little interest in the Resource Acceleration Option,” the group said in a letter to regulators, which would deliver electricity at a premium cost without providing the benefit of regulatory surplus-based environmental attributes that would be useful in meeting corporate environmental, social, and governance goals.”

Cause for hope? 

While advocates see little good in the commission’s approval of the Green Source Advantage Choice program, they still have some faint cause for hope.

One is the so-called Clean Transition Tariff, which Duke could propose later this year. An outgrowth of a May agreement between the utility and Amazon, Google, Microsoft, and Nucor, that program could allow participating customers to spur new projects, such as solar–battery storage combos or small nuclear energy, that provide carbon-free electricity around the clock.

This is not within the order,” said Jimenez, but the May memorandum of understanding, is the big opportunity for something better.”

Duke says the Clean Transition Tariff would be another voluntary option for customers, not a replacement for the one just greenlighted. We see the approval of Green Source Advantage Choice as a first step,” the company’s Stewart said, enabling us to move forward with new tariffs like the Clean Transition Tariff.”

Maggie Shober, research director at the Southern Alliance for Clean Energy, agrees the memorandum of understanding is cause for some optimism. But she also notes that it’s only an agreement to talk about something. It could be an opportunity,” she said, or it could be a missed opportunity. “

And no matter what, the Clean Transition Tariff won’t cater to municipalities and other midsize customers with climate commitments. If these customers decline to pursue Green Source Advantage Choice, their only option is to wait for Duke to adjust.

Commissioner Jeffrey A. Hughes pointed to that possibility in a concurring opinion.

Once the program offerings are launched, it will quickly become clear whether the program is as attractive as Duke asserts,” Hughes wrote. If concerns continue and interest is modest from the outset, it is my hope that Duke will work quickly on new programs that will have a greater impact.”

Read the full story here.
Photos courtesy of

The Navajo Nation said no to a hydropower project. Trump officials want to ensure tribes can’t do that again.

The U.S. Energy Secretary said allowing tribes to weigh in on energy projects on their land creates "unnecessary burdens to the development of critical infrastructure."

Early last year, the hydropower company Nature and People First set its sights on Black Mesa, a mountainous region on the Navajo Nation in northern Arizona. The mesa’s steep drop offered ideal terrain for gravity-based energy storage, and the company was interested in building pumped-storage projects that leveraged the elevation difference. Environmental groups and tribal community organizations, however, largely opposed the plan. Pumped-storage operations involve moving water in and out of reservoirs, which could affect the habitats of endangered fish and require massive groundwater withdrawals from an already-depleted aquifer.  The Federal Energy Regulatory Commission, which has authority over non-federal hydropower projects on the Colorado River and its tributaries, ultimately denied the project’s permit. The decision was among the first under a new policy: FERC would not approve projects on tribal land without the support of the affected tribe. Since the project was on Navajo land and the Navajo Nation opposed the project, FERC denied the permits. The Commission also denied similar permit requests from Rye Development, a Florida-based company, that also proposed pumped-water projects. Now, Department of Energy Secretary Chris Wright wants to reverse this policy. In October, Wright wrote to FERC, requesting that the commission return to its previous policy and that giving tribes veto power was hindering the development of hydropower projects. The commission’s policy has created an “untenable regime,” he noted, and “For America to continue dominating global energy markets, we must remove unnecessary burdens to the development of critical infrastructure, including hydropower projects.”  Wright also invoked a rarely used authority under the Federal Powers Act to request that the commission make a final decision no later than December 18. And instead of the 30 to 60 days generally reserved for proposed rule changes, the FERC comment period was open for only two weeks last month. If his effort proves successful, hydropower projects like the ones proposed by Nature and People First could make a return to the Navajo Nation regardless of tribal support.  More than 20 tribes and tribal associations largely in the Southwest and Pacific Northwest, environmental groups, and elected officials, including Representative Frank Pallone, a Democrat from New Jersey, sent letters urging FERC to continue its current policy. “Tribes are stewards of the land and associated resources, and understand best how to manage and preserve those resources, as they have done for centuries,” wrote Chairman William Iyall of the Cowlitz Indian Tribe in Washington in a letter submitted to the commission.  Tó Nizhóní Ání, or TNA, a Diné-led water rights organization based in Black Mesa on the Navajo Nation, also submitted comments opposing the proposed hydropower project. In the 1960s, after Peabody Coal broke up sections of the resource-rich region between the Hopi and Navajo tribes for mining, the company was accused of misrepresenting the conditions of its operations and the status of mineral rights to local communities. Environmental problems soon followed, as the company’s groundwater pumping exceeded legal limits, compromising the aquifer and access to drinking water. According to Nicole Horseherder, Diné, and TNA’s executive director, this led residents of Black Mesa to use community wells. “They were now starting to have to haul all their water needs in this way,” she said. “That really changed the lifestyle of the people on Black Mesa.”  After the coal mines closed 20 years later, Black Mesa communities have focused on protecting their water resources while building a sustainable economy. But when Nature and People First’s founder Denis Payre presented the company’s plans, he seemed unaware of the tribes’ history in the region. During these presentations, Payre also made promises that if the company’s hydropower project went forward, it would benefit residents. The project would generate 1,000 jobs during construction and 100 jobs permanently, he claimed, and would help locals readily access portable drinking water. “He wasn’t understanding that our region has a history of extraction, and that is coal mining and its impact on our groundwater,” said Adrian Herder, Diné, TNA’s media organizer. “It seemed like this individual was tugging at people’s heartstrings, [saying] things that people wanted to hear.” If the commission decides to retract tribes’ ability to veto hydropower projects, it will mark a shift in the relationship between Indigenous nations and the federal government. Horseherder described such a move as the “first step in eroding whatever’s left between [these] relationships.” She is pessimistic about the commission’s decision and expects it will retract the current policy.  “The only thing I’m optimistic about is that Indigenous people know that they need to continue to fight,” she said. “I don’t see this administration waking up to their own mistakes at all.”  This story was originally published by Grist with the headline The Navajo Nation said no to a hydropower project. Trump officials want to ensure tribes can’t do that again. on Dec 10, 2025.

Georgia hashes out plan to let data centers build their own clean energy

Big companies have spent years pushing Georgia to let them find and pay for new clean energy to add to the grid, in the hopes that they could then get data centers and other power-hungry facilities online faster. Now, that concept is tantalizingly close to becoming a reality, with regulators, utility Georgia Power,…

Big companies have spent years pushing Georgia to let them find and pay for new clean energy to add to the grid, in the hopes that they could then get data centers and other power-hungry facilities online faster. Now, that concept is tantalizingly close to becoming a reality, with regulators, utility Georgia Power, and others hammering out the details of a program that could be finalized sometime next year. If approved, the framework could not only benefit companies but also reduce the need for a massive buildout of gas-fired plants that Georgia Power is planning to satiate the artificial intelligence boom.Today, utilities are responsible for bringing the vast majority of new power projects online in the state. But over the past two years, the Clean Energy Buyers Association has negotiated to secure a commitment from Georgia Power that ​“will, for the first time, allow commercial and industrial customers to bring clean energy projects to the utility’s system,” said Katie Southworth, the deputy director for market and policy innovation in the South and Southeast at the trade group, which includes major hyperscalers like Amazon, Google, Meta, and Microsoft. The ​“customer-identified resource” (CIR) option will allow hyperscalers and other big commercial and industrial customers to secure gigawatts of solar, batteries, and other energy resources on their own, not just through the utility. The CIR option isn’t a done deal yet. Once Georgia Power, the Public Service Commission, and others work out how the program will function, the utility will file a final version in a separate docket next year. And the plan put forth by Georgia Power this summer lacks some key features that data center companies want. A big point of contention is that it doesn’t credit the solar and batteries that customers procure as a way to meet future peaks in power demand — the same peaks Georgia Power uses to justify its gas-plant buildout. But as it stands, CEBA sees ​“the approved CIR framework as a meaningful step toward the ​‘bring-your-own clean energy’ model,” Southworth said — a model that goes by the catchy acronym BYONCE in clean-energy social media circles. Opening up the playing field for clean energy The CIR option is technically an addition to Georgia Power’s existing Clean and Renewable Energy Subscription (CARES) program, which requires the utility to secure up to 4 gigawatts of new renewable resources by 2035. CARES is a more standard ​“green tariff” program that leaves the utility in control of contracting for resources and making them available to customers under set terms, Southworth explained. Under the CIR option, by contrast, large customers will be able to seek out their own projects directly with a developer and the utility. Georgia Power will analyze the projects and subject them to tests to establish whether they are cost-effective. Once projects are approved by Georgia Power, built, and online, customers can take credit for the power generated, both on their energy bills and in the form of renewable energy certificates. Georgia Power’s current plan allows the procurement of up to 3 gigawatts of customer-identified resources through 2035. Letting big companies contract their own clean power is far from a new idea. Since 2014, corporate clean-energy procurements have surpassed 100 gigawatts in the United States, equal to 41% of all clean energy added to the nation’s grid over that time, according to CEBA. Tech giants have made up the lion’s share of that growth and have continued to add more capacity in 2025, despite the headwinds created by the Trump administration and Republicans in Congress. But most of that investment has happened in parts of the country that operate under competitive energy markets, in which independent developers can build power plants and solar, wind, and battery farms. The Southeast lacks these markets, leaving large, vertically integrated utilities like Georgia Power in control of what gets built. Perhaps not coincidentally, Southeast utilities also have some of the country’s biggest gas-plant expansion plans. A lot of clean energy projects could use a boost from power-hungry companies. According to the latest data from the Southern Energy Renewable Association trade group, more than 20 gigawatts of solar, battery, and hybrid solar-battery projects are now seeking grid interconnection in Georgia. “The idea that a large customer can buy down the cost of a clean energy resource to make sure it’s brought onto the grid to benefit them and everybody else, because that’s of value to them — that’s theoretically a great concept,” said Jennifer Whitfield, senior attorney at the Southern Environmental Law Center, a nonprofit that’s pushing Georgia regulators to find cleaner, lower-cost alternatives to Georgia Power’s proposed gas-plant expansion. ​“We’re very supportive of the process because it has the potential to be a great asset to everyone else on the grid.” Isabella Ariza, staff attorney at the Sierra Club’s Beyond Coal Campaign, said CEBA deserves credit for working to secure this option for big customers in Georgia. In fact, she identified it as one of the rare bright spots offsetting a series of decisions from Georgia Power and the Public Service Commission that environmental and consumer advocates fear will raise energy costs and climate pollution.

Renowned Astronomers Push to Protect Chile's Cherished Night Sky From an Industrial Project

Chile’s Atacama Desert is one of the darkest spots on earth, a crown jewel for astronomers who flock from around the world to study the origins of the universe in this inhospitable desert along the Pacific coast

SANTIAGO, Chile (AP) — Chile’s Atacama Desert is one of the darkest spots on earth, a crown jewel for astronomers who flock from around the world to study the origins of the universe in this inhospitable desert along the Pacific coast.“It's a perfect cocktail for astronomy,” said Daniela González, executive director of the Skies of Chile Foundation, a nonprofit that defends the quality of the country’s night skies. A private company is pressing ahead with plans to construct a giant renewable energy complex in sight of one of Earth’s most productive astronomical facilities — the Paranal Observatory, operated by an international consortium known as the European Southern Observatory, or ESO.In the letter, 30 renowned international astronomers, including Reinhard Genzel, a 2020 Nobel laureate in astrophysics who conducted much of his prize-winning research on black holes with the ESO-operated telescopes in the Atacama Desert, describe the project as “an imminent threat” to humanity's ability to study the cosmos, and unlock more of its unknowns.“The damage would extend beyond Chile’s borders, affecting a worldwide scientific community that relies on observations made at Paranal to study everything from the formation of planets to the early universe,” the letter reads. “We are convinced that economic development and scientific progress can and must coexist to the benefit of all people in Chile, but not at the irreversible expense of one of Earth’s unique and irreplaceable windows to the universe.”The scientists join a chorus of voices that have been urging the Chilean government to relocate the hydrogen-based fuel production plant since the plan was unveiled a year ago by AES Andes, an offshoot of the American-based multinational AES Corp. In response to a request for comment, AES Corp. said that its own technical studies showed the project would be “fully compatible” with astronomical observations and compliant with the Chilean government's strict regulations on light pollution. "We encourage trust in the country’s institutional strength, which for decades has guaranteed certainty and environmental protection for multiple productive sectors," the company said.The plan, which is still under environmental review, calls for 3,000 hectares (7,400 acres) of wind and solar energy farms, a desalination plant and a new port. That means not only a major increase in light pollution but also new dust, ground vibrations and heightened atmospheric turbulence that blurs stars and makes them twinkle. All of that — just three kilometers (miles) from the Paranal Observatory’s high-powered telescopes — will mess the view of key astronomical targets and could obstruct scientific advances, experts say. “At the best sites in the world for astronomy, stars don't twinkle. They are very stable, and even the smallest artificial turbulence would destroy these characteristics,” said Andreas Kaufer, the director of operations at ESO, which assesses that the AES project would increase light pollution by 35%.“If the sky is becoming brighter from artificial light around us, we cannot do these observations anymore. They're lost. And, since we have the biggest and most sensitive telescopes at the best spot in the world, if they're lost for us, they're lost for everyone." “Major observatories have been chased out to remote locations, and essentially now they’re chased out to some of the last remaining dark sky locations on Earth, like the Atacama Desert, the mountain peaks of Hawaii, areas around Tucson, Arizona,” said Ruskin Hartley, the executive director of DarkSky International, a Tuscon-based nonprofit founded by astronomers. “All of them are now at risk from encroaching development and mining. It’s happening everywhere.”DeBre reported from Buenos Aires, Argentina Copyright 2025 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.Photos You Should See – Nov. 2025

New control system teaches soft robots the art of staying safe

MIT CSAIL and LIDS researchers developed a mathematically grounded system that lets soft robots deform, adapt, and interact with people and objects, without violating safety limits.

Imagine having a continuum soft robotic arm bend around a bunch of grapes or broccoli, adjusting its grip in real time as it lifts the object. Unlike traditional rigid robots that generally aim to avoid contact with the environment as much as possible and stay far away from humans for safety reasons, this arm senses subtle forces, stretching and flexing in ways that mimic more of the compliance of a human hand. Its every motion is calculated to avoid excessive force while achieving the task efficiently. In MIT Computer Science and Artificial Intelligence Laboratory (CSAIL) and Laboratory for Information and Decisions Systems (LIDS) labs, these seemingly simple movements are the culmination of complex mathematics, careful engineering, and a vision for robots that can safely interact with humans and delicate objects.Soft robots, with their deformable bodies, promise a future where machines move more seamlessly alongside people, assist in caregiving, or handle delicate items in industrial settings. Yet that very flexibility makes them difficult to control. Small bends or twists can produce unpredictable forces, raising the risk of damage or injury. This motivates the need for safe control strategies for soft robots. “Inspired by advances in safe control and formal methods for rigid robots, we aim to adapt these ideas to soft robotics — modeling their complex behavior and embracing, rather than avoiding, contact — to enable higher-performance designs (e.g., greater payload and precision) without sacrificing safety or embodied intelligence,” says lead senior author and MIT Assistant Professor Gioele Zardini, who is a principal investigator in LIDS and the Department of Civil and Environmental Engineering, and an affiliate faculty with the Institute for Data, Systems, and Society (IDSS). “This vision is shared by recent and parallel work from other groups.”Safety firstThe team developed a new framework that blends nonlinear control theory (controlling systems that involve highly complex dynamics) with advanced physical modeling techniques and efficient real-time optimization to produce what they call “contact-aware safety.” At the heart of the approach are high-order control barrier functions (HOCBFs) and high-order control Lyapunov functions (HOCLFs). HOCBFs define safe operating boundaries, ensuring the robot doesn’t exert unsafe forces. HOCLFs guide the robot efficiently toward its task objectives, balancing safety with performance.“Essentially, we’re teaching the robot to know its own limits when interacting with the environment while still achieving its goals,” says MIT Department of Mechanical Engineering PhD student Kiwan Wong, the lead author of a new paper describing the framework. “The approach involves some complex derivation of soft robot dynamics, contact models, and control constraints, but the specification of control objectives and safety barriers is rather straightforward for the practitioner, and the outcomes are very tangible, as you see the robot moving smoothly, reacting to contact, and never causing unsafe situations.”“Compared with traditional kinematic CBFs — where forward-invariant safe sets are hard to specify — the HOCBF framework simplifies barrier design, and its optimization formulation accounts for system dynamics (e.g., inertia), ensuring the soft robot stops early enough to avoid unsafe contact forces,” says Worcester Polytechnic Institute Assistant Professor and former CSAIL postdoc Wei Xiao.“Since soft robots emerged, the field has highlighted their embodied intelligence and greater inherent safety relative to rigid robots, thanks to passive material and structural compliance. Yet their “cognitive” intelligence — especially safety systems — has lagged behind that of rigid serial-link manipulators,” says co-lead author Maximilian Stölzle, a research intern at Disney Research and formerly a Delft University of Technology PhD student and visiting researcher at MIT LIDS and CSAIL. “This work helps close that gap by adapting proven algorithms to soft robots and tailoring them for safe contact and soft-continuum dynamics.”The LIDS and CSAIL team tested the system on a series of experiments designed to challenge the robot’s safety and adaptability. In one test, the arm pressed gently against a compliant surface, maintaining a precise force without overshooting. In another, it traced the contours of a curved object, adjusting its grip to avoid slippage. In yet another demonstration, the robot manipulated fragile items alongside a human operator, reacting in real time to unexpected nudges or shifts. “These experiments show that our framework is able to generalize to diverse tasks and objectives, and the robot can sense, adapt, and act in complex scenarios while always respecting clearly defined safety limits,” says Zardini.Soft robots with contact-aware safety could be a real value-add in high-stakes places, of course. In health care, they could assist in surgeries, providing precise manipulation while reducing risk to patients. In industry, they might handle fragile goods without constant supervision. In domestic settings, robots could help with chores or caregiving tasks, interacting safely with children or the elderly — a key step toward making soft robots reliable partners in real-world environments. “Soft robots have incredible potential,” says co-lead senior author Daniela Rus, director of CSAIL and a professor in the Department of Electrical Engineering and Computer Science. “But ensuring safety and encoding motion tasks via relatively simple objectives has always been a central challenge. We wanted to create a system where the robot can remain flexible and responsive while mathematically guaranteeing it won’t exceed safe force limits.”Combining soft robot models, differentiable simulation, and control theoryUnderlying the control strategy is a differentiable implementation of something called the Piecewise Cosserat-Segment (PCS) dynamics model, which predicts how a soft robot deforms and where forces accumulate. This model allows the system to anticipate how the robot’s body will respond to actuation and complex interactions with the environment. “The aspect that I most like about this work is the blend of integration of new and old tools coming from different fields like advanced soft robot models, differentiable simulation, Lyapunov theory, convex optimization, and injury-severity–based safety constraints. All of this is nicely blended into a real-time controller fully grounded in first principles,” says co-author Cosimo Della Santina, who is an associate professor at Delft University of Technology. Complementing this is the Differentiable Conservative Separating Axis Theorem (DCSAT), which estimates distances between the soft robot and obstacles in the environment that can be approximated with a chain of convex polygons in a differentiable manner. “Earlier differentiable distance metrics for convex polygons either couldn’t compute penetration depth — essential for estimating contact forces — or yielded non-conservative estimates that could compromise safety,” says Wong. “Instead, the DCSAT metric returns strictly conservative, and therefore safe, estimates while simultaneously allowing for fast and differentiable computation.” Together, PCS and DCSAT give the robot a predictive sense of its environment for more proactive, safe interactions.Looking ahead, the team plans to extend their methods to three-dimensional soft robots and explore integration with learning-based strategies. By combining contact-aware safety with adaptive learning, soft robots could handle even more complex, unpredictable environments. “This is what makes our work exciting,” says Rus. “You can see the robot behaving in a human-like, careful manner, but behind that grace is a rigorous control framework ensuring it never oversteps its bounds.”“Soft robots are generally safer to interact with than rigid-bodied robots by design, due to the compliance and energy-absorbing properties of their bodies,” says University of Michigan Assistant Professor Daniel Bruder, who wasn’t involved in the research. “However, as soft robots become faster, stronger, and more capable, that may no longer be enough to ensure safety. This work takes a crucial step towards ensuring soft robots can operate safely by offering a method to limit contact forces across their entire bodies.”The team’s work was supported, in part, by The Hong Kong Jockey Club Scholarships, the European Union’s Horizon Europe Program, Cultuurfonds Wetenschapsbeurzen, and the Rudge (1948) and Nancy Allen Chair. Their work was published earlier this month in the Institute of Electrical and Electronics Engineers’ Robotics and Automation Letters.

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